Electric furnace



Nov. 17, 1936. A. E. RHOADS 2,061,090

ELECTRIC FURNACE I Filed Nov. 16, 1935 s Sheets-Sheet 1 If 34 I 1, 7

@1661"! d: Pleads.

NOV. 17, 1936. V E RHOADS 2,061,090

ELECTRIC FURNACE- Filed Nov. 16, 1933 3 Sheets-Sheet 3 d/er/ 5 P404 afa.

Patented Nov. 17, 1936 UNITED STATES PATENT OFFICE ELECTRIC FURNACEApplication November 16, 1933, Serial No. 698,284

9 Claims.

This invention relates in general to electric furnaces and is moreparticularly concerned with an improved construction wherein the maximumthermal energy resulting from the transformation into heat, by the aidof the electric arc, of

the electric energy may be most efliciently utilized in metallurgicaloperations, such as the melting of iron and other metals.

It is an object of the hereindescribed invention to provide an electricfurnace of the type utilizing a plurality of pairs of electrodes, suchas in a multi-phase furnace, wherein each pair of electrodes togetherwith its feeding mechanism is assembled and mounted in such a manner asto constitute a 'unit which may be replaced by a spare unit orinterchanged with the other units of the furnace.

A further object is to provide an electric furnace of the oscillating orrocking type which is 2 constructed in such a manner as to enable theelectrodes to be disposed at such an angle in relation to the anglebetween the limits of oscillation for a predetermined load, that themelting of the metal will be carried on most efficiently and therefractory wall of the furnace will be washed a maximum amount by themolten metal.

It is also an object to provide improved means for feeding theelectrodes, which are so arranged as to not only move the electrodes inan axial 3O direction, but also simultaneously cause the electrodes tobe rotated, whereby the electrodes will be prevented from becomingcemented in their bearings by the condensed fumes of volatile metals.This rotation of the electrodes also pre- 35 vents the possibility ofthe electrodes sagging should they become soft under the intense heat ofthe furnace, and, when considered in connection with the proper angulardisposition of the electrodes, also causes the electrode points at thearc to be symmetrically maintained and thus assure a proper position ofthe arc.

Still another object is to provide an electric furnace of the electrodetype wherein the electrodes are so mounted as to permit of a maxi- 45mum charge of unmelted metal and in which the electrode tips are removedfrom the charging door, thereby lessening the possibility of theelectrodes becoming damaged during the charging operation.

In accordance with the general features of this invention, it isproposed to provide a cylindrical melting chamber which is supported foroscillation or rotation about its longitudinal axis. The furnace isprovided in a portion of its wall with aligned removable sections. Thecharging door and electrodes are supported on these sections. Each pairof electrodes is supported to form a V and is mounted on one of theremovable sections to form a unit structure which may be interchangedwith one of the other sections 5 supporting a similar pair of electrodesor may be replaced by a spare service unit. Each unit is provided with amotor which is connected through a driving mechanism so as tosimultaneously feed the electrodes of each unit in a longi- 10 tudinaldirection. Moreover, cam means are provided for rotating the electrodesin response to their longitudinal movement. The cam means are soarranged that rather than cause the electrodes to rotate continuously inone direction, 15 which would necessitate a sliding or slip type ofelectrical connection to the electrodes, the electrodes are rotatedfirst 360 degrees in one direction and then reversed and rotated 360degrees in the opposite direction. This arrangement obviates thenecessity of a slip connection and enables the cables to be securelyclamped to the electrodes.

Other objects and features of this invention will more fully appear fromthe following detail description taken in connection with theaccompanying drawings which illustrate several embodiments thereof, andin which:

Figure l is a fragmentary cross-sectional view taken through a furnaceof the character described and embodying the features of this invention;

Figure 2 is a fragmentary longitudinal section of the same, takensubstantially on the line II-II of Figure 1;

Figure 3 is an enlarged fragmentary sectional view through one of theelectrode supports, taken substantially on the line III-III of Figure 2;

Figure 4 is a detail view showing the development of the cam surface forrotating one of the electrodes;

Figure 5 is a view diagrammatically showing a modified arrangement ofelectrodes in the furnace;

Figure 6 is a view diagrammatically showing an alternative arrangementof the modification shown in Figure 5.

Figure '7 is a schematic view showing the electrical connections to theelectrodes; and

Figures 8 and 9 are views diagrammatically showing the relationshipbetween the angle between a pair of electrodes and the angle lyingbetween the points of maximum oscillation of the furnace.

As shown on the drawings:

In order that an electrical furnace of the herein described type shalloperate most efficlently, it has been found desirable to keep the massof the furnace, per unit of charge, as low as possible. In so doing, theamount of electrical energy required to bring the furnace proper up totemperature is maintained at a low value. For such purpose, the furnaceshould be of a cylindrical shape.

The furnace, as illustrated in Figure 1, comprises an outer metallicshell ll! of cylindrical shape which is provided with a refractorylining l I. This shell is supported upon a pair of spaced groovedrollers l2 and 13 which are rotatably supported in brackets l4 and I5, apair of these rollers being placed at each end of the furnace so as tosupport the furnace with its longitudinal axis in a horizontal position,although where maximum mixing is required, the axis may be eccentricallymounted, as shown in the patent to Crosby, No. 1,336,820, issued April13, 1920. Movement of the furnace is guided by means of a rail 16whichis secured to the cylindrical shell so as to engage the groovedpulleys. Adjacent the rail 16 is a curved rack I'I having teeth whichare in engagement with a pinion I8. This pinion is rotatable with ashaft l9 which is connected through an automatic reversing mechanismwith a shaft 20 of a driving motor 2|.

The reversing mechanism may be of any suitable type, but shouldpreferably be of the type which will automatically drive the pinion l8to rock or oscillate the furnace in one direction a predetermined amountand then reverse to cause the furnace to move in the other direction apredetermined amount. Such mechanisms are usually adjustable so that themovement of the furnace may be regulated as desired, and are alsousually so arranged that they may be manually operated to move thefurnace, as, for example, during the pouring operation.

As clearly shown in Figure 1, the shell [0 does not form a closedmetallic shell, but the ends are in spaced relation to leave alongitudinally extending opening 22 in the furnace for mounting theelectrode units. The ends of the shell ID are deflected to formoutwardly extending flanges 23 and 24.

The opening 22 is closed by a plurality of removably secured plates orsections 25 and 26 which are respectively adapted to support a pair ofelectrodes and a charging door. In the illustrated furnace, the platesor sections 25 and 26 are alternately arranged with the outermostsections 2525 separated from a central section 25 by means of sections26-26 disposed on either side of the central section 25. The sections 25are interchangeable and the sections 26 are also interchangeable witheach other.

The ends of the plates or sections 25 and 26 respectively project pastthe flanges 23 and 24 and are secured to the shell in the same manner.The end to be secured cooperates with a series of clamping bolts 21which extend through appropriate slots 28 and are provided with clampingnuts 29. Each clamping screw or lug is pivoted at its inner end so thatwhen the clamping nut is released, the lug may be swung out of clampingposition, thereby releasing the ends of the plate. The joints betweenthe shell l0 and the plates 25 and 26 are sand sealed. For this purpose,a flange 30 extends along each of the flanges 23 and 24 in spacedrelation thereto to form a cavity for receiving the sand which is toform the seal. It will be observed that when one of these plates isclamped into position, the sand in this cavity engages the inner surfaceof the plate and forms a seal. The interior of each of the removablymounted plates is provided with refractory material II, the inner endsof which cooperate with the inner ends of the refractory material H toform the interior of the melting chamber. In removing one of theseplates, the refractory material supported thereby would also be removed.

Referring to Figure 2, it will be observed that the same type of seal isprovided for connecting the lateral edges of the plates 25 and 26 toeach other and to the furnace. The only difference is that, where thesections are to be secured together or to the furnace, the flanged edgesof the plates are in abutment rather than overlapping, and the clampingbolts cooperate with a circumferentially extending band 3| which isclamped against the sand within the respective containers along theedges of the plates.

Each section 25 not only forms a portion of the furnace shell but alsoserves the purpose of providing a support for each pair of electrodestogether with the electrode feeding mechanism. In other words, each pairof electrodes mounted on a section 25 forms a complete unit which may beinterchanged with any other electrode unit of the furnace or may bereplaced by a spare unit when necessary. The electrodes of each pair aremounted to form a V with the converging ends of the electrodes disposedwithin the melting chamber. Each electrode in its passage through therefractory material and the outer shell of the furnace, formed by theplate 25, is slidably supported in a bushing 33 of insulating material.In order to support the outer end of the carbon electrode and the Weightof the electric cable 34, which is clampingly secured to the outer endof the carbon by a clamp 35, a bracket 36 is provided. This bracket hasa central hub portion 31 which surrounds the electrode and a pluralityof radial and downwardly deflected legs or supports 38 which are securedat their lower ends to the plate 25, as by bolts 39.

Rotatably and slidably supported for axial movement in the hub 31 is asplit sleeve 40 which is provided With cut-out portions 4| and 42 in itsperiphery to define opposed flanges 43 and 44 disposed respectively oneach side of the split of the sleeve. A clamping bolt 45 withcooperating nut 46 extends thru apertures in these flanges. With thisarrangement, the sleeve may be clamped to the electrode 32, and, sincethe head of this bolt and the nut 46 are countersunk or disposed in thecut-out portions adjacent the flanges 43 and 44, it is possible for thesleeve to rotate within the hub 31 without interference. The lower endof this sleeve is extended to define a cylindrical shell 41 whichsurrounds the electrode. The outer surface of this shell is providedwith circumferentially extending threads 48 and the inner surface isradially spaced from the surface of the electrode to define acylindrical socket 49 which is open at the lower end of the shellportion.

Longitudinal or axial feed of the electrode is attained by means of aworm wheel 50 which is secured to and rotatable with a shaft 5|, thisshaft being rotatably supported on one of the legs 38 of the bracket 36.The upper end of this shaft is connected by means of a pair of bevelgears 52 and 53 to a main shaft 54 which is rotatably supported uponbearing brackets 5555 of the two Iii. i

supporting brackets 3646 of the electrodes which constitute a pair. Thebracket 55 may, if desired, be integrally formed with the bracket 38.The other end of the shaft 54 is connected through a similar pair ofbevel gears to the longitudinal feeding mechanism of the other electrodeof the pair. The common shaft 54 is driven through a pair of suitablegears 56 and 51, the former being carried by the shaft 54 and the latterby the driving shaft of a motor 58, this motor being supported in anydesired manner, as for example, on a bracket 59 which may be integrallyformed with one of the brackets 36. This arrangement enables each pairof electrodes to be simultaneously fed in an axial direction as thepoints are consumed, whereby the arc is maintained at a fixed distancefrom the metal which is being melted.

For causing the electrodes to rotate simultaneously with theirlongitudinal feed, the shell 41 of each electrode assembly is providedwith an inwardly extending pin 60 which is disposed near the open end ofthe socket 49 and projects thereinto. cooperatively associated with thispin is a cylindrical sleeve 6| which surrounds the electrode and issecured at its lower end to the plate 25 in any appropriate manner. Thissleeve is of such length that when the shell portion 41 is at itsuppermost limit of travel, the upper end of the sleeve BI extends intothe open end of the socket 49. The outer surface of the sleeve BI isprovided with a spiral groove I52 for receiving the projecting end ofthe pin 50. Referring to Fig. 4 showing a development of the sleeve 6|,it will be observed that the groove 62 is so arranged that when theelectrode is longitudinally moved, the pin 60 will follow the groove 62and, due to the pitch of the groove, will cause the sleeve together withthe electrode to which it is clamped to be rotated through 360. At theend of this rotation, the groove is reversed and spiraled in theopposite direction, whereby the electrode will be rotated in theopposite direction 360. Although in the present structure the groove isillustrated as being designed to rotate the electrode through twocomplete revolutions in opposite directions, it may be found desirableto increase the number of rotations in certain types of installations.This rotation of the electrode is advantageous in that, when volatilemetals are being melted, there is little liability of the electrodebecoming cemented in the bushing where it passes through the furnacewall, due to the vapor from the volatile metal. Moreover, the rotationalso tends to prevent sagging of the electrodes due to their becomingsoft from the intense heat within the furnace, and the points of theelectrodes will also be symmetrically consumed, thus maintaining the arcin proper position for giving a high efliciency.

In Fig. 1, the electrodes constituting each pair are disposed so as tolie in a plane at right angles to the longitudinal center line of themelting chamber. As an alternative and modified arrangement, theelectrodes of each pair may be supported on the associated plate 25 asshown in Fig. 5, where the plane of each pair of electrodes is disposedat an angle to the longitudinal center line of the melting chamber. Thisarrangement is advantageous in that it enables a shortening of theplates 25 and 26, whereby the rocking or oscillating angle of thefurnace may be increased so as to wash a greater amount of therefractory wall thereof. Further, since the plane of the electrodes isbrought more nearly into alignment with the center line of the furnace,the initial charge of metal to be melted may be more easily extended upon each side of the plane of the electrodes without interference. It isalso contemplated, as an alternative electrode arrangement, that theplanes of the pairs of electrodes may be brought into alignment orparallel relationship with the longitudinal axis of the furnace, inwhich case the respective pairs may be circumferentially ofiset relativeto the furnace, as shown in Figure 6. Such an arrangement has theadvantage that. the electrodes will be further disposed from thecharging door, thus decreasing the likelihood of the portions of theelectrodes within the melting chamber becoming damaged during thecharging operation.

The charging door may be of any suitable construction and is preferablymounted in one of the plates 26. Since it is preferable to provide twocharging door plates, the second plate may contain a charging door ornot, a desired. Since charging doors for furnaces of this type are sowell known in the art, it has not been deemed necessary to illustratethe charging door. However, it is preferred that the inner opening tothe pouring spout, which is usually constructed as a part of thecharging door, be coincident with the joint between the refractorymaterial I I and the refractory material II, since the pouring spout isusually left open to form a vent, and it is undesirable to have themelted metal wash the joint between the refractory portions I I and II.In other words, the maximum angle of rotation of the furnace isdetermined by the joint just described.

While the features of this invention have been described in connectionwith a multi-phase, in this case three-phase, furnace, it is obviousthat these features may be readily incorporated in a furnace foroperating on two-phase or singlephase current. For three-phaseoperation, the electrodes may be connected as illustrated in Figure 7,or the three pairs of electrodes may be fed from individualtransformers, thus in effect giving three single-phase furnaces in asingle shell. Any desired connection of transformer windings may beused, depending upon the electrical source available. In Figure 7, atransformer 63 is shown with a Y connected primary connected to therespective conductors of a three-phase distribution circuit 64. Thesecondary windings of the transformer are connected in delta and to eachof the corresponding electrodes of each pair. The other electrodes ofeach pair are interconnected by a common connection 65.

Figures 8 and 9 diagrammatically illustrate the feature of thisinvention, whereby it is possible to build a furnace of this type havingan exceedingly high efficiency. As previously pointed out, the furnacehas a cylindrical melting chamber which enables as large an area of therefractory lining as possible to be washed by the melted metal, thus notonly cooling the lining but also raising the temperature of the chargeby means of the heat abstracted from the lining. It will, therefore, beevident that the maximum rock of the furnace and thus the maximum washof the lining will be determined by the joints between the refractoryportions II and II, or, in other words, at the flanges 23 and 24 asshown in Figure 1.

It is also desirable to direct the arc towards the metal, rather thantoward the lining, and, to this end, it is desirable that, at themaximum angle of rock, the arc end of the lowermost electrode shall beno further away from the surface of the metal than is the remainder ofthe electrode. Of course, it will be appreciated that the arc should beas close to the metal as possible, in order to reduce the amount ofradiant heat falling upon the unwashed refractory between theelectrodes.

In the consideration of the foregoing desiderata, which are the primaryfactors having a bearing on the furnace efilciency, it has been foundthat a definite relationship exists for a given load line or levelbetween the angle defined by the electrodes of each pair and the anglebetween the refractory joints or the points defining the maximum rock ofthe furnace, both of these angles being about the same center, in thiscase the longitudinal axis of the furnace, this axis also being the axisabout which it is rocked.

Referring to Figure 8, let it be assumed that the furnace is desired tobe most eflicient in its operation when the load level is at thelongitudinal axis of the melting chamber. Then, in order to get theelectrode points as close as possible to the metal they would have to besubstantially in contact with it. Now, if lines 66 and 61 are drawn fromthe longitudinal axs of the furnace as a center, through the most widelyspaced points of the electrode points to the interior wall of therefractory as represented by the arc H-l l 'I I, the angle A will bedefined. Another angle, angle B, is now constructed by similarprocedure, by drawing the lines 68 and 69 through the joints between therefractory portion l I and refractory portions ll--Il, designated as 23and 24. In this case, the angle A is found to be greater than the angleB and it will not be possible to secure a maximum wash of the refractorywall, the difference between the angles A and B being represented by theshaded portion. The greatest wash obtainable would, therefore, be whenthe level of the metal coincides with the lines 66 and 61. Any furtheror increased rocking would cause the electrodes to dip into the metal,which, of course, is objectionable.

Referring now to Figure 9, it will be observed that if the electrodesare raised so as to have the are too great a distance from the metal,the angle A then becomes smaller than the angle B, as shown by theshaded portions. Under these conditions the amount of furnace rocking isdetermined and limited by the joints 23 and 24, but the furnace will notoperate at its greatest efficiency because the arc is further from themetal than is necessary.

It is, therefore. apparent that in order to obtain the most efiicientarrangement, the angles A and B should be equal or preferably angle Ashould be slightly less than the angle B. Thus it will be possible toget the are as close as possible to the metal and at the same time beable to wash as much of the refractory lining as possible.

It will also be apparent from Figure 9 that, if the electrodes areplaced with their axes substantially parallel to the lines 68 and 69,and these axes are considered instead of the angle A, then the closestarc could be placed to the metal, without the electrodes limiting themaximum wash of the refractory, would be when the axes are spaced fromthe lines 68 and 69 a distance substantially equal to the radius of anelectrode.

Although the foregoing description in regard to the relationshipexisting between angle A and angle B has been confined to the conditionwherein the load level is coincident with the longitudinal center lineof the melting chamber, this relationship also holds true for other loadlevels as well.

From the foregoing description, it will be apparent that thehereindescribed invention provides an improved electric furnace of therocking type having novel means for feeding the electrodes in alongitudinal direction and simultaneously rotating the electrodes; afurnace in which each pair of electrodes is associated and mounted onthe furnace in such a way as to form an interchangeable r replaceableunit; which is so designed and constructed as to enable electrodes to bedisposed at such an angle in relation to the angle between the limits ofrocking for a predetermined load that the melting of the metal will becarried on most efiiciently and the refractory wall of the furnace willbe washed a maximum amount; and wherein the electrodes are so mounted asto permit of a maximum charge of unmelted metal, the electrode tipsbeing so disposed as to substantially avoid the possibility of damagingthe same when the furnace is initially charged.

Now, it is, of course, to be understood that although I have describedin detail several embodiments of my invention, the invention is not tobe thus limited but only insofar as defined by the scope and spirit ofthe appended claims.

I claim as my invention:

1. In a furnace having a closure structure de fining a melting chamber,a removable section defining a portion of said structure, a pair ofelectrodes supported on said section and projecting into said chamber,means to feed said electrodes in an axial direction, and means to rotatesaid electrodes in response to their axial movement, said section,electrodes, feed means and rotating means being associated in such amanner as to form a unitary assembly.

2. In a furnace, a unitary assembly comprising a supporting member, apair of electrodes projecting through said member, means to axially feedsaid electrodes, and cam means responsive to the axial movement forrotating the electrodes in one direction and then in the reversedirection.

3. A multi-phase electric furnace of the character described comprisingan elongated melting chamber, and spaced pairs of electrodes alignedlongitudinally of the melting chamber and extending thereinto, theplanes of the respective pairs of electrodes being substantially inparallel relationship and at an oblique angle to the longitudinal axisof the melting chamber.

4. In an electric furnace having a closure structure defining asubstantially cylindrical melting chamber with its longitudinal axisdisposed substantially horizontally and arranged to be rockedsubstantially about said axis, a removably secured segmental sectionforming a part of said structure and having joints therewithcircumferentially spaced of said chamber, a pair of electrodes supportedon said section and arranged in a V with their converging ends adjacentthe longitudinal axis of the furnace, the maximum angle at the widestportion of the electrode points measured at the longitudinal axis of thechamber being substantially equal to the angle lying between the jointsof said section measured at the same axis.

5. In an electric furnace having a closure structure defining asubstantially cylindrical melting chamber with its longitudinal axisdisposed substantially horizontally and arranged to be rockedsubstantially about said axis, a removably secured segmental sectionforming a part of said structure and having joints therewithcircumferentially spaced of said chamber, a pair of electrodes supportedon said section and arranged in a V with their converging ends adjacentthe longitudinal axis of the furnace, the maximum angle at the widestportions of the electrode points taken at the longitudinal axis of thechamber being less than the angle lying between the joints of saidsection in said structure.

6. In an electric furnace having a closure struc-- ture defining asubstantially cylindrical melting chamber with its longitudinal axisdisposed substantially horizontally and arranged to be rockedsubstantially about said axis, a removable section in said structureforming a portion thereof, the joints of said section with the otherportion of said structure being circumferentially spaced relative tosaid chamber and determining the maximum area of wash of the interior ofthe chamber during the rocking thereof, a pair of electrodes carried bysaid section disposed in a V with their converging ends contiguous thelongitudinal axis of the melting chamber, the angle between thelowermost portions of the electrodes at the rocking limits of thechamber being less than the angle between the joints of said sectiontaken with the longitudinal axis of the chamber as a center.

'7. In an electric furnace having a closure structure defining asubstantially cylindrical melting chamber with its longitudinal axisdisposed substantially horizontally and arranged to be rockedsubstantially about said axis, a removable section forming a portion ofsaid structure, the joints of said section with the other portion ofsaid structure being circumferentially spaced relative to said chamberand determining the maximum area of Wash of the interior of the chamberduring the rocking thereof, a pair of electrodes carried by said sectiondisposed in a V with their converging ends contiguous the longitudinalaxis of the chamber, the respective axes of said electrodes beingsubstantially parallel to lines drawn from the longitudinal axis of saidchamber through the respective joints of said section and the otherportion of said structure, and spaced from said lines an amountsubstantially equal to the radius of an electrode.

8. In an electric furnace having a closure structure defining asubstantially cylindrical melting chamber with its longitudinal axisdisposed substantially horizontally and arranged to be rockedsubstantially about said axis, a removably secured segmental sectionforming a part of said structure and having joints therewithcircumferentially spaced of said chamber, a pair of electrodes supportedon said section and arranged in a V with their converging ends adjacentthe longitudinal axis of the furnace, the maximum angle at the widestportion of the electrode points measured at the longitudinal axis of thechamber being substantially no greater than the angle lying between thejoints of said section measured at the same axis.

9. In a furnace having a casing with a refractory wall defining amelting chamber provided with an opening, a removable unitary structureadapted to provide a closure for the opening, said removable unitarystructure comprising a refractory wall section, a pair of electrodessupported on said section and movable therethrough to project into themelting chamber, and power feed means for moving said electrodes mountedon said section and connected to said electrodes.

ALBERT E. RHOADS.

